As a method of conveying a light-weight conveyance object or a heavy conveyance object, one in which the conveyance object is conveyed by using a plurality of belt conveyor apparatuses arranged along a conveyance route of the conveyance object, is generally employed. As one of such belt conveyor apparatuses, there is a curved belt conveyor apparatus for changing a conveyance direction of a conveyance object. The curved belt conveyor apparatus is an apparatus in which an endless fan-shaped belt is wound around two end pulleys (a head pulley and a tail pulley) which are pivotally supported by an apparatus frame with an opening angle of 90 degrees, for example, provided therebetween. In particular, in order to change a conveyance direction of a light-weight and small-sized conveyance object, each of two end pulleys is required to have a small diameter for making the conveyance object transfer to an upstream or downstream conveyor. When such a curved belt conveyor is driven to travel the fan-shaped belt, a circumferential speed on an inside diameter side, being a side close to a pivot of the fan-shaped belt, and a circumferential speed on an outside diameter side, are different, so that it is often the case where both of a head pulley and a tail pulley being end pulleys are set as driven pulleys, and for each of the pulleys, there are used short pulleys with straight outer cylinders which are rotatably provided in a parallel manner by being externally fitted to a center shaft.
Further, in a curved belt conveyor apparatus, two end pulleys are arranged with a predetermined opening angle of 90 degrees, for example, provided therebetween, so that tension toward a pivot side, namely, an inside diameter side of a fan-shaped belt (tension in an inside diameter direction) is inevitably generated with respect to the fan-shaped belt. Therefore, when a curved belt conveyor apparatus is driven by providing a driving device at an intermediate position of the apparatus, thereby traveling a fan-shaped belt, the fan-shaped belt is displaced in the inside diameter direction due to tension in the inside diameter direction applied to the fan-shaped belt, and both of a head pulley and a tail pulley are slipped out of an endless belt which surrounds the pulleys from a forward side and a return side of the fan-shaped belt, which definitely causes slip between the end pulley and a rear surface of the fan-shaped belt.
In order to solve such problems, there is a technique in which, for example, a timing belt is attached to a rear surface of an outside-diameter-side end portion (outer peripheral edge portion) of a fan-shaped belt, a sprocket is provided to a head pulley at an outside diameter portion of the fan-shaped belt to drive the timing belt, the head pulley and a tail pulley are set as driven pulleys, and for each of the pulleys, there are used short pulleys with straight outer cylinders which are turnably provided in a parallel manner by being externally fitted to a center shaft, and there is devised a curved belt conveyor apparatus in which a plurality of fastening elements with which shoulder portions of the timing belt attached to the rear surface of the outside-diameter-side end portion of the fan-shaped belt are pulled and fastened from the rear surface toward the outside diameter direction of the fan-shaped belt (idling rollers abutted against a front surface of the fan-shaped belt, and fastening rollers abutted against the shoulder portions of the timing belt attached to the rear surface of the fan-shaped belt) are provided with a predetermined angle interval provided therebetween, and by pulling the fan-shaped belt in the outside diameter direction being an opposite direction of the inside diameter direction toward a pivot, the fan-shaped belt is prevented from being displaced in the inside diameter direction (refer to Patent Document 1). Further, other than the above, there is also devised a curved belt conveyor apparatus in which there is provided a turning mechanism including a driving rotation member having a toothed belt which endlessly turns between an outer peripheral edge portion of a belt part on a forward side of a fan-shaped belt and an outer peripheral edge portion of a belt part on a return side of the fan-shaped belt, and which is covered by a plurality of blocks embedded with magnets at an outer peripheral portion thereof, and driven rotation members having toothed belts which endlessly turn on the outside of belt on the forward side of the fan-shaped belt and on the outside of belt on the return side of the fan-shaped belt, respectively, and each of which is covered by a plurality of blocks embedded with magnets at an outer peripheral portion thereof, and when a driving mechanism drives the driving rotation member, the magnets of the blocks covered with respect to the toothed belt of the driving rotation member are made to attract the magnets of the blocks covered with respect to the toothed belts of the driven rotation members to travel the fan-shaped belt while sandwiching the fan-shaped belt, thereby preventing the fan-shaped belt from being displaced in an inside diameter direction (refer to Patent Document 2).
Patent Document 1: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2011-520726
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2007-106595